ioctl command value for updating also was different, I believe: 0x4040462e (or, at least, it's so in geekmaster's video player).

I don't think there are still owners of pre-5.1.0 devices, so it's just an interesting fact. But if you want to differentiate pre-5.1.0 devices: firmware version could be read from /etc/prettyversion.txt on device.

P.S. Oh, I see this "old" structure is already present in include/mxcfb.h as mxcfb_update_data.